In response to the development of compact and light weight electronic information products, the semiconductor manufacturing process is now aimed to enable high-density and automated production. On the other hand, the currently available electronic information products are designed to have a touch sensing surface or touchscreen that is gradually increased in size. As a result, the conductive electrodes for the touchscreen originally made of an indium tin oxide (ITO) material are now replaced by metal conductive electrodes. To avoid the metal conductive electrodes formed on a substrate of the touchscreen from being visually perceived by a user, it is a target of the research and development engineers in the touchscreen industry to develop metal conductive electrodes having a very small width.
FIG. 1 is a pictorial description of a conventional method of manufacturing metal conductive electrodes 10. In a first step, a layer of material for forming metal conductive electrodes 10 is adhered to a substrate 12 via at least one adhesion layer 11, which is also referred to as a bonding layer, so that the metal conductive electrodes 10 formed later does not easily separate from the substrate 12. In a second step, at least one weatherproof layer 13, which is also referred as an anti-corrosion layer, is covered on the layer of material for forming metal conductive electrodes 10. In a third step, a wet etching process using an etching fluid is conducted, so that the weatherproof layer 13, the layer of material for forming metal conductive electrodes 10 and the adhesion layer 11 are etched to form an electrode circuit 14 consisting of a plurality of metal conductive electrodes 10. Finally, the entire surfaces of the electrode circuit 14 are covered with an optically clear adhesive (OCA) film 16.
Please refer to FIG. 2, the adhesion layer 11 formed according to the above conventional metal conductive electrode manufacturing method includes two sublayers, namely, an intermediate layer 17 connected to the substrate 12 and an electrically conductive seed layer 18 connected to the layer of material for forming metal conductive electrodes 10.
The wet etching is isotropic. Since the weatherproof layer 13 is formed of an etch-resistant material, there is a relatively large difference between the etching rates of the etching fluid on the weatherproof layer 13 and on the layer of material for forming metal conductive electrodes 10. Moreover, the weatherproof layer 13 formed in the second step usually has a non-uniform thickness. As a result, when the etching fluid vertically etches the weatherproof layer 13, the layer of material for forming metal conductive electrodes 10 and the adhesion layer 11, a serious side etching 15 will occur on the metal conductive electrodes 10 formed in the wet etching process.
In other words, when being viewed sidewardly as shown FIG. 1, the side etching 15 tends to occur on the lateral surfaces of the metal conductive electrodes 10 so formed, particularly when the metal conductive electrodes 10 have a designed width smaller than 5 μm and a designed thickness larger than 0.3 μm. As a result, the total etched surface on each of the metal conductive electrodes 10 is too large in proportion to the total area thereof, and the metal conductive electrodes 10 are unevenly etched to result in increased electric impedance of the electrode circuit 14. In some worse conditions, the electrode circuit 14 formed of the metal conductive electrodes 10 will break locally. Therefore, the metal conductive electrodes 10 are not easily controllable in quality and have low yield rate to form a tough problem in manufacturing very fine conductive electrodes.
Moreover, in view that the metal conductive electrodes 10 currently widely used to form the electrode circuit 14 all have a very small width, it is necessary to further provide the metal conductive electrodes 10 with some protection measure, so that the electrode circuit 14 is not easily oxidized after being used in the working environment over a long period of time and does not lose its intended operating performance, allowing the touchscreen produced with the metal conductive electrodes 10 to have prolonged service life, good yield rate and environmental durability.
In addition, all the manufactured touchscreens are subjected to a series of strict environmental durability tests. For example, the touchscreens are subjected to a high temperature of 85° C. and a 90% relative humidity for 1000 hours in a high-temperature heating test; and are boiled at 100° C. for 100 minutes to simulate the use of the touchscreens in a high-temperature and high-pressure environment for an extended time period.
During the above two tests, water molecules permeating through the optically clear adhesive film 16 to contact with the metal conductive electrodes 10 tend to cause oxidation of the metal conductive electrodes 10. Therefore, when the touchscreens using the metal conductive electrodes 10 manufactured with the conventional method have been used over a long time, their capacitive sensors might very possibly have a largely increased impedance value and could not operate in a normal state.
It is therefore tried by the inventor to overcome the drawbacks of the metal conductive electrodes 10 manufactured in the conventional method.